Positive electrode material and nickel-zinc battery

ABSTRACT

The present invention provides a nickel-zinc battery of an inside-out structure, that is, a battery comprising a positive electrode containing beta-type nickel oxyhydroxide and a negative electrode containing zinc and having a similar structure to an alkali manganese battery, in which the beta-type nickel oxyhydroxide consists of substantially spherical particles, mean particle size of which is within a range from 19 μm to a maximum of 40 μm, the bulk density of which is within a range from 1.6 g/cm 3  to a maximum of 2.2 g/cm 3 , tap density of which is within a range from 2.2 g/cm 3  to a maximum of 2.7 g/cm 3 , specific surface area which based on BET method is within a range from 3 m 2 /g to a maximum of 50 m 2 /g, and the positive electrode of the nickel zinc battery contains graphite powder, where the weight ratio of graphite powder against a total weight of the positive electrode is defined within a range from 4% to a maximum of 8%.

RELATED APPLICATION DATA

The present application is a divisional of application Ser. No.09/838,453, filed Apr. 19, 2001, now U.S. Pat. No. 6,686,091, which isincorporated herein by reference to the extent permitted by law.

BACKGROUND OF THE INVENTION

The present invention relates to beta-type nickel oxyhydroxide and amethod of producing thereof, and yet, also relates to a positiveelectrode active material composed of beta-type nickel oxyhydroxide.Further, the present invention relates to a nickel-zinc batteryincorporating a positive electrode comprising beta-type nickeloxyhydroxide as a positive electrode active material and a negativeelectrode comprising zinc as a negative electrode active material.

In recent years, compact-size portable electronic apparatuses,especially portable game players, digital cameras and digitalvideo-camera recorders, or the like, have been propagated verysignificantly. It is expected that these compact-size portableelectronic apparatus will be propagated furthermore from now on, andthus, demand for compact-size battery serving as a power-supply sourcefor these compact-size portable electronic apparatuses will also bepromoted quickly. Generally, any of those compact-size portableelectronic apparatuses utilizes a high operating voltage and requires alarge amount of current, and thus, a usable power source must bedistinguished in discharge characteristic under heavy load.

Of those batteries satisfying the above requirements, such aalkaline-manganese battery has already been propagated most widely,which comprises manganese dioxide for composing the positive electrodeand zinc for the negative electrode, and yet, it also comprises highlyconcentrated alkaline aqueous solution for composing electrolyticsolution. Inasmuch as manganese dioxide and zinc are respectivelyinexpensive, and yet, because of high energy density per weight, notonly for the power-supply source of compact-size portable electronicapparatuses, but the alkaline-manganese battery is also utilizedextensively.

Considering further utility for compact-size portable electronicapparatuses and in order to further improve discharge characteristicunder heavy load, a wide variety of improvements have been achieved in arange from battery material to the composition of battery itself.However, in the above alkaline-manganese battery, inasmuch as a positiveelectrode active material comprising manganese dioxide performsdischarge based on homogeneous solid-phase chemical reaction, as aresult of discharge, voltage gradually lowers whereby drawing such adischarge curve of downward-sloping. Because of this, in such acompact-size portable electronic apparatus requiring a high voltage anda large amount of current, basically, discharge performance of thealkaline-manganese battery can hardly suffice practical need, and yet,despite of a variety of improvements thus far effected, duration ofactually operable capacity of such a compact-size portable electronicapparatus has thus been extended by a negligible extent. Further, any ofthe modern compact-size portable electronic apparatuses is apt toperform own operation with a relatively higher voltage and a greateramount of current in the initial stage of distribution in the market. Todeal with this tendency, it is imperative that such a battery compatiblewith a newer model of any of compact-size portable electronicapparatuses and capable of preserving distinguished durability to heavyload be provided as essential requirements.

To suffice the above requirements, a nickel-zinc battery has thus beenproposed. The nickel-zinc battery comprises its positive electrodecomprising nickel oxyhydroxide and its negative electrode comprisingzinc, which contains such an operating voltage and durability to heavyload respectively being higher than those of the abovealkaline-manganese battery. On the other hand, nickel oxyhydroxide as apositive electrode active material easily generates oxygen and a largeamount of self-discharge as problems to solve. As a method for solvingthese problems, for example, the Japanese Laid-Open Patent PublicationNo. HEISEI-10-214621 (1998) proposes such a nickel-zinc battery havingan “inside-out” type structure with a less amount of self-discharge byutilizing gamma-type nickel oxyhydroxide (γ —NiOOH) for composing apositive electrode active material.

Such a battery utilizing the above-cited gamma-type nickel oxyhydroxidehas a small amount of self-discharge, and has higher operating potentialthan that of an alkaline manganese battery. However, it is a problemthat such a battery cannot have large discharge capacity because theabove gamma-type nickel oxyhydroxide has relatively low density.

SUMMARY OF THE INVENTION

The object of the present invention is to provide such a nickel-zincbattery having such a discharge voltage higher than that of analkaline-manganese battery and distinguished in the large-currentdischarge characteristic.

The present invention introduces such a positive electrode activematerial comprising beta-type nickel oxyhydroxide consisting ofsubstantially spherical particles. Preferably, mean particle size of thebeta-type nickel oxyhydroxide is within a range from 19 μm to a maximumof 40 μm. Preferably, bulk density of the beta-type nickel oxyhydroxideis within a range from 1.6 g/cm³ to a maximum of 2.2 g/cm³. Preferably,tap density is within a range from 2.2 g/cm³ to a maximum of 2.7 g/cm³.Preferably, specific surface area of beta-type nickel oxyhydroxide basedon BET method is within a range from 3 m²/g to a maximum of 50 m²/g.

The above-referred beta-type nickel oxyhydroxide for composing thepositive electrode active material used for implementing the presentinvention is previously treated with alkaline aqueous solution andcontains alkaline cation between layers of the beta-type nickeloxyhydroxide.

Further, the nickel-zinc battery proposed by the present inventionutilizes the above-referred beta-type nickel oxyhydroxide for composingpositive electrode active material. The positive electrode at leastcontains beta-type nickel oxyhydroxide and graphite powder, where theweight ratio of graphite powder against a total weight of the positiveelectrode is defined within a range from 4% to a maximum of 8%.

According to the present invention, it is possible to secure such nickeloxyhydroxide with least self-discharge, and yet, such a nickel-zincbattery using said nickel oxyhydroxide for composing positive electrodeactive material as the one embodied by the invention generates such anoperating voltage and distinguished durability to heavy loadrespectively being higher than those of conventional alkaline-manganesebatteries.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical cross-sectional view of a nickel-zinc batteryaccording to a practical form for embodying the present invention;

FIG. 2 is explanatory of substantially spherical beta-type nickeloxyhydroxide (A) realized by the present invention and conventionalnon-spherical beta-type nickel oxyhydroxide (B);

FIG. 3 exemplifies grading distribution of the beta-type nickeloxyhydroxide according to a practical form for embodying the presentinvention;

FIGS. 4A to 4D exemplify the relationship between the composition ofpotassium in nickel oxyhydroxide after completing a process for treatingthe beta-type nickel oxyhydroxide with aqueous solution of potassiumhydroxide and the diffraction figure of powder via X-ray analysis;

FIG. 5 exemplifies discharge curve when sample batteries 1˜4 eachcontaining 1500 mW of power executed discharge down to 1.0 V;

FIG. 6 exemplifies results of testing digital cameras loaded with samplebatteries 1 to 4;

FIG. 7 exemplifies the relationship between specific surface area anddischarge capacity of the positive electrode active material shown bysample batteries 5 to 20;

FIG. 8 exemplifies the relationship between specific surface area anddischarge capacity of the positive electrode active material shown bysample batteries 21 to 24,

FIG. 9 exemplifies the relationship between specific surface area anddischarge capacity of the positive electrode active material shown bysample batteries 25 to 28;

FIG. 10 exemplifies the relationship between specific surface area anddischarge capacity of the positive electrode active material shown bysample batteries 29˜39;

FIG. 11 is a table showing compositions of the sample batteries 1 to 4;

FIG. 12 is a table showing discharge capacities of the sample batteries1 to 4;

FIG. 13 is a table showing the classification and the battery propertiesof the sample batteries 5 to 28;

FIG. 14 is a table showing processing conditions for the samplebatteries 29 to 39;

FIG. 15 is a table showing compositions of the sample batteries 29 to39;

FIG. 16 is a table showing discharge capacities of the sample batteries29 to 39 before storage;

FIG. 17 is a table showing discharge capacities of the sample batteries29 to 39 after storage;

FIG. 18 is a table showing compositions of the sample batteries 40 to48;

FIG. 19 is a table showing discharge capacities of the sample batteries40 to 48; and

FIG. 20 exemplifies the relationship between graphite contents in thepositive-polar composing material and discharge capacity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Practical forms for implementing the present invention in relation tobeta-type nickel oxyhydroxide and method of producing the nickeloxyhydroxide, a positive electrode active material, and a nickel-zincbattery, are described below.

FIG. 1 is a vertical cross-sectional view of a nickel-zinc battery 1 asan example of a battery according to an embodiment of the presentinvention. The nickel-zinc battery 1 comprises the following: a batterycan 2, a positive electrode 3, a separator 4, a negative electrodemixture 5, a sealing member 6, a washer 7, a negative electrode terminalplate 8, and a current collecting pin 9.

The battery can 2 is made of iron plated with nickel, for example, whichconstitutes an external positive electrode terminal of the nickel-zincbattery 1.

The positive electrode 3 is of a hollow cylindrical form. Beta-typenickel oxyhydroxide, graphite powder as electrically conductive agent,and electrolytic aqueous solution of potassium hydride jointly formulatepositive electrode mixture. The positive electrode mixture is moldedinto a hollow cylindrical form to prepare positive electrode pellets 3a, 3 b, and 3 c, which are serially laminated inside of the battery can2.

The separator 4 is of hollow cylindrical form and disposed inside of thepositive electrode 3.

The negative electrode mixture 5 comprises zinc particles for composinga negative electrode active material, electrolytic solution usingaqueous solution of potassium hydride, and gelling agent which initiallygels the negative electrode mixture 5 and then causes zinc particles tobe dispersed in the electrolytic solution evenly.

The battery can 2 internally stores the positive electrode 3 and theseparator 4 filled with the negative electrode mixture 5. An aperture ofthe battery can 2 is coupled with the sealing member 6 for sealing theaperture. The sealing member 6 is made of plastic material. Further, byway of concealing the sealing member 6, the washer 7 and the negativeelectrode terminal plate 8 are secured to the sealing member 6. Further,the current collecting pin 9 made of brass is inserted into athrough-hole of the sealing member 6 secured with the washer 7 from theupper position.

By way of inserting the nail-form current-collecting pin 9 welded to thenegative electrode terminal plate 8 into a through-hole formed at thecenter of the sealing member 6, the current-collecting pin 9 reaches thenegative electrode mixture whereby enabling the negative electrode tocollect current. By way of connecting the positive electrode 3 to thebattery can 2, the positive electrode can collect current. Externalcircumferential surface of the battery can 2 is fully concealed by anexternal label (not shown). A positive electrode terminal is positionedto the bottom of the battery can 2.

The inventive battery comprising the above structural componentsgenerates own positive electrode reaction, negative electrode reaction,total reaction, and theoretical electromotive force by way of thefollowing:

-   Positive electrode reaction: NiOOH+H₂O+e⁻→Ni(OH)₂+OH⁻E₀=0.49V-   Negative electrode reaction: Zn+20H⁻→ZnO+H₂O+2e⁻E₀=−1.25V-   Total reaction: 2NiOOH+Zn+H₂O→2Ni(OH)₂+ZnO-   Theoretical electromotive force: E₀=1.74V

As is clear from the above chemical formulas, nickel hydride and zincoxide are respectively generated from nickel oxyhydroxide and zinc viadischarge reaction.

Nickel oxyhydroxide for composing a positive electrode active materialis used for composing activating material of secondary batteries such asa nickel-hydrogen battery and a nickel-cadmium battery. It is well knownthat these batteries proved surpassing discharge performance. Nickeloxyhydroxide includes two kinds consisting of beta-type and gamma-type.Normally, these components can easily be generated by way ofelectrolytically oxidizing nickel hydroxide via so-called electrolyticoxidizing method. Nevertheless, the synthesized nickel oxyhydroxide, inparticular, the beta-type nickel oxyhydroxide generates substantialself-discharge to result in the generation of oxygen gas, and thus, interms of storage characteristic and resistant characteristic againstleakage of electrolytic solution, the beta-type nickel oxyhydroxide isnot desired for use. To compensate for this, in order to use thebeta-type nickel oxyhydroxide for composing active material of theprimary batteries, it is essential that self-discharge rate be loweredeffectively. As a solution for this, conventionally, gamma-type nickeloxyhydroxide with less self-discharge rate has been used against thebeta-type nickel oxyhydroxide.

It is conceived that self-discharge and the resultant generation ofoxygen are caused by decomposition of ion substance such as NO₃ ⁻ andCO₃ ²⁻ present in its crystal occurred inside of the battery. Such anion substance remains inside of crystal as impurities in the course ofproducing nickel oxyhydroxide. It is conceived however thatself-discharge characteristic of nickel oxyhydroxide can be improved byway of decreasing the above impurities.

On the other hand, it is also conceived that the deterioration of thestorage characteristic of nickel oxyhydroxide is caused by dilutedelectrolytic solution, where dilution of electrolytic solution is causedby solidification of alkaline cation present in the electrolyticsolution within lattice via infiltration of alkaline cation betweenlayers of nickel oxyhydroxide relative to passage of time. Note thatnickel oxyhydroxide itself is multi-layer compound constituted withcadmium iodide crystals.

Based on the above conception, according to the findings of inventors,initially, by applying a chemical oxidizing method to cause nickeloxyhydroxide to be oxidized in chemical solution containing a suitableoxidizing agent such as sodium hypochlorite and a suitable alkalinesubstance such as lithium hydroxide, sodium hydroxide, and potassiumhydroxide, for example, nickel oxyhydroxide was synthesized.

It was found that, in the course of synthesizing nickel oxyhydroxide,independently of the kind including gamma and beta types, theabove-referred ion of impurities flowed into the synthesizing solutionfrom the crystals to result in the generation of such nickeloxyhydroxide with decreased self-discharge characteristic and improvedsuitability for composing active material of the primary batteries.

Oxidation reaction generated in the above experiment is expressed by wayof the following:2Ni(OH)₂+ClO⁻→2NiOOH+Cl⁻+H₂O

Note that, depending on pH value in the chemical solution, type of theresultant nickel oxyhydroxide differs. More particularly, when the pHvalue is less than a certain value, high-density beta-type nickeloxyhydroxide with 4.68 g/cm³ of theoretical density is generated. On theother hand, when the pH value exceeds a certain value, low-densitygamma-type nickel oxyhydroxide with 3.79 g/cm³ of theoretical density isgenerated. In the nickel-zinc battery 1 related to the presentinvention, in order to secure a greater capacity for the battery, amongthe above-referred nickel oxyhydroxides generated via the above-referredchemical oxidizing method, it is preferred that high-density beta-typenickel oxyhydroxide be used for composing positive electrode activematerial.

It is further desired that high-density nickel hydroxide comprisingsubstantially spherical particles be used for a starting raw material.Normally, conventional nickel hydroxide comprises non-sphericalparticles each having 1.4˜1.8 g/cm³ of tap density and 1.0˜1.4 g/cm³ ofbulk density. On the other hand, the above-referred high-density nickelhydroxide comprises substantially spherical particles each having2.0˜2.5 g/cm³ of tap density and 1.4˜1.8 g/cm³ of bulk densityrespectively being higher than those of conventional nickel hydroxide.

Method of measuring the tap density and the bulk density is describedbelow. Initially, objective powder particles are fed into a specificcontainer via natural fall. Assuming that mass is expressed by A(g),volume B(cm³), and another volume is C(cm³) after softly tapping bottomof the lifted container 200 times against a desk, then, the bulk densityand the tap density are defined by formulas shown below.

Bulk density=A/B (g/cm³)

Tap density=A/C (g/cm³)

It is desired that the tap density and the bulk density of beta-typenickel oxyhydroxide for forming positive electrode active materialspecified in the embodiment of the present invention shall remain in arange defined below. More particularly, the tap density of the beta-typenickel oxyhydroxide shall remain in a range of 2.2˜2.7 g/cm³, whereasthe bulk density of the beta-type nickel oxyhydroxide shall remain in arange of 1.6˜2.2 g/cm³. This is because, if the tap density and the bulkdensity remain less than the lower limit values, it is quite difficultto expand discharge capacity, and yet, it is quite difficult to producesuch beta-type nickel oxyhydroxide having greater values of the tapdensity and the bulk density beyond the upper limit of the definedranges.

FIG. 2A exemplifies the inventive beta-type nickel oxyhydroxidecomprising substantially spherical particles. FIG. 2B exemplifiesconventional beta-type nickel oxyhydroxide comprising non-sphericalparticles. The upper side shown in FIGS. 2A and 2B designatesphotographs of the inventive beta-type nickel oxyhydroxide and theconventional beta-type nickel oxyhydroxide taken via an electronicmicroscope. Photographs shown in the lower side designate external formof particles shown in the upper side.

As shown in FIG. 2A, the inventive beta-type nickel oxyhydroxidecomprises substantially spherical particles. More particularly, particlesurface is relatively smooth without presence of projections. Althoughthere are some of slender and flat particles, as a whole, particles aresubstantially spherical.

On the other hand, as shown in FIG. 2B, conventional beta-type nickeloxyhydroxide comprises non-spherical particles showing such a formcrushed into powder from a large mass, where each particle is squarish,and yet, there are a variety of forms including flat form, slender form,and substantially cubic form.

FIG. 3 exemplifies an example of grading distribution of the inventivebeta-type nickel oxyhydroxide. It is desired that the inventivebeta-type nickel oxyhydroxide for composing a positive electrode activematerial for implementing the present invention shall remain within sucha mean particle size and a grading distribution specified below. Moreparticularly, it is desired that the inventive beta-type nickeloxyhydroxide shall remain in a range of 19˜40 μm of mean particle size.This is because, if the mean particle size is less than 19 μm or beyond40 μm, it causes production of batteries to become quite difficult. Itis further desired that the inventive beta-type nickel oxyhydroxideshall remain in a range of 5˜80 μm of the grading distribution.

It is further desired that mean particle size of the beta-type nickeloxyhydroxide shall remain in a range of 19˜25 μm and the gradingdistribution shall remain in a range of 5˜70 μm.

Here, minimum and maximum values of the grading distribution are definedas follows: when 5% of the entire grading values are a value or lessthan the value, the value is defined to be the minimum value, and when95% of the entire grading value are a value or less than the value, thevalue is defined to be the maximum value.

When producing the beta-type nickel oxyhydroxide in accordance with theabove method by applying high-density nickel hydroxide as a starting rawmaterial, it is possible to produce such nickel hydroxide with highertap density and higher bulk density to facilitate expansion of batterycapacity.

Further, it is also desired that specific surface area of the beta-typenickel oxyhydroxide based on the BET method shall remain in a range of3˜50 m²/g. If the specific surface area based on the BET method is lessthan 3 m²/g., it will result in the difficulty to expand dischargecapacity when discharging large current in particular. Conversely, ifthe specific surface area based on the BET method exceeds 50 m²/g., eventhe beta-type nickel oxyhydroxide has a relatively large amount ofself-discharge, which results in difficulty in securing sufficientstorage characteristic.

Further, by way of mixing beta-type nickel oxyhydroxide yielded fromnickel hydroxide via chemical oxidation process with such an aqueoussolution (devoid of oxidizing agent) comprising one kind among lithiumhydroxide, sodium hydroxide, and potassium hydroxide, or two kinds ormore than two kinds selected therefrom, and then, by causing alkalinecation to infiltrate into interface of layers of beta-type nickeloxyhydroxide, the inventors discovered that such beta-type nickeloxyhydroxide having such a storage characteristic surpassing that ofconventional beta-type nickel oxyhydroxide was secured while preservinghigh-density proper to the beta-type nickel oxyhydroxide.

It is desired that composition of alkaline cation in the beta-typenickel oxyhydroxide generated via the above method shall remain in arange of 2˜5% by weight. It is further preferred that the composition ofalkaline cation shall remain in a range of 3˜5% by weight. If thecomposition is less than 2% by weight, then, the amount of alkalinecation infiltrated between layers of the beta-type nickel oxyhydroxidewill become short whereby storage characteristic can hardly be improved.Although a greater amount of alkaline cation may be able to infiltratebetween layers by applying higher pressure via an autoclave, forexample, if the composition of alkaline cation exceeds 5% by weight,then, the above beta-type nickel oxyhydroxide will be transmuted intolow-density gamma-type nickel oxyhydroxide to lose own high-density ofthe positive electrode active material.

FIG. 4 exemplifies the relationship between the composition of potassiumin the beta-type nickel oxyhydroxide after being treated with aqueoussolution of potassium hydroxide and the diffraction figure of powder viaan X-ray treatment.

The X-ray diffraction patterns shown in FIG. 4A and FIG. 4B designatepatterns of the beta-type nickel oxyhydroxide. These drawings representthat nickel oxyhydroxide still preserves the beta-form when the contentsof potassium ion is less than 5% by weight. The X-ray diffractionpatterns shown in FIG. 4C and FIG. 4D designate patterns of thegamma-type nickel oxyhydroxide. It is thus understood that the beta-typenickel oxyhydroxide is transmuted into the gamma-type nickeloxyhydroxide when the contents of potassium ion exceeds 6% by weight.

When utilizing nickel oxyhydroxide as a positive electrode activematerial, there is a technical problem to solve because nickeloxyhydroxide and nickel hydroxide generated from nickel oxyhydroxide viadischarge respectively contain a low degree of electron conductivity.Accordingly, in order to promote utility of the positive electrodeactive material, it is preferred to mix graphite powder with thepositive electrode mixture. On the other hand, when forming such anickel-zinc battery comprising “inside-out” structure by way ofproviding external circumference of the nickel-zinc battery with apositive electrode comprising the blend of nickel oxyhydroxide at leastmixed with graphite powder formed into a hollow-cylindricalconfiguration in particular, and yet, by way of providing the centerportion with a gelled negative electrode comprising the blend of zincfor composing negative electrode active material, electrolytic solution,which are at least mixed with gelling agent, and yet, by way of furtherdisposing a separator between the positive electrode and the negativeelectrode, inventors discovered that desirable contents of graphitepowder against total weight of the positive electrode ranged from 4% byweight to a maximum of 8% by weight.

When there is less than 4% by weight of the contents of graphite powder,it will not be able to fully improve electron conductivity in thepositive electrode. On the other hand, when there is more than 8% byweight of the contents of graphite powder, although electronconductivity in the positive electrode can be promoted to full extent,amount of nickel oxyhydroxide to be filled in the positive electrode asactivating material decreases to result in the contracted capacity ofthe battery. By way of properly arranging the contents of graphitepowder to be mixed in the positive electrode mixture, the nickel-zincbattery 1 realized by the present invention can secure optimal electronconductivity and storage capacity throughout service life.

EXAMPLE

Next, concrete examples for implementing the present invention aredescribed below. It should be understood however that the scope of thepresent invention is not solely limited to the following examples.

First, physical characteristics of nickel oxyhydroxide are describedbelow.

Initially, by way of chemically oxidizing electrolyzed manganese dioxideand high-density nickel hydroxide, a first beta-type nickel oxyhydroxidewas generated. The above high-density nickel hydroxide was composed ofsubstantially spherical particles based on 2.3 g/cm³ of tap density and1.8 g/cm³ of bulk density. The above first beta-type nickel oxyhydroxidewas composed of substantially spherical particles based on 2.5 g/cm³ oftap density; 2.0 g/cm³ of bulk density, 20 μm of mean particle size; and5˜70 μm of grading distribution. The above chemical oxidation wasexecuted in alkaline solution containing sodium hypochlorite. Next, agamma-type nickel oxyhydroxide was generated by chemically oxidizing inthe same manner as described above. The above gamma-type nickeloxyhydroxide was composed of substantially spherical particles based on1.8 g/cm³ of tap density and 1.6 g/cm³ of bulk density. Next a secondbeta-type nickel oxyhydroxide was generated by chemically oxidizing agamma-type nickel oxyhydroxide and conventional nickel hydroxide. Thesecond beta-type nickel oxyhydroxide was composed of non-sphericalparticles based on 1.8 g/cm³ of tap density and 1.4 g/cm³ of bulkdensity. Next, based on the composition specified in FIG. 11, the firstbeta-type nickel oxyhydroxide, the gamma-type nickel oxyhydroxide, thesecond beta-type nickel oxyhydroxide, graphite particles, and 40% byweight of aqueous solution of potassium hydride, were fully mixed witheach other to complete formulation of the positive electrode activeagent. Next, the prepared positive electrode active agents werepressurized by applying identical condition to mold them into a hollowcylindrical configuration before completing the positive electrodesrelated to the present invention. Note that the mixed graphite had 6 μmof mean particle size, 1˜25 μm of grading distribution, and a maximum of0.3% by weight of ash component, as formulated into high-purity powderparticles.

Initially, the positive electrode component was inserted in a batterycan. Next, a separator comprising a polyolefin non-woven fabric completewith hydrophilic treatment was inserted into the positive electrodecomponent. After feeding about 1 g of electrolytic solution, gellednegative electrode mixture comprising mixture of zinc, gelling agent,and electrolytic solution was further inserted into the battery can.Finally, aperture of the battery can was sealed with a sealing memberattached with a washer and a current-collecting pin before completingproduction of alkaline batteries conforming to “AA”-size format assamples 1˜4.

FIG. 11 represents composition (% by weight) of component materials forconstituting the positive electrode and filling amount (g) of positiveelectrode mixture per nickel-zinc battery. Sample 1 represents analkaline-manganese battery. Sample 2 represents a nickel-zinc batteryusing beta-type nickel oxyhydroxide generated via chemical oxidation ofhigh-density nickel hydroxide (this is referred to as a first betanickel-zinc battery henceforth). Sample 3 represents a nickel-zincbattery using gamma-type nickel oxyhydroxide generated via chemicaloxidation of high-density nickel hydride (this is referred to as a gammanickel-zinc battery henceforth). Sample 4 represents a nickel-zincbattery using beta-type nickel oxyhydroxide generated via chemicaloxidation of conventional nickel hydroxide (this is referred to as asecond beta nickel-zinc battery). Note that filling amount of positiveelectrode mixture per battery differs between respective samples. Thisis because density of the used positive electrode active materialdiffers between respective samples.

Next, those batteries corresponding to samples 1˜4 were subject to adischarge test and a loading test. The discharge test was conducted byway of executing discharge until battery voltage descended to 1.0V at1500 mW of constant power. To execute the loading test, commerciallyavailable digital cameras (“CAMEDIA C-2000 ZOOM” with a zoom lens, aproduct and a registered trade name of Olympus Optical Co., Ltd., Tokyo,Japan, each being fitted with a LCD monitor screen and using four of“AA”-size batteries), were utilized. The loading test was executed bycounting the number of still shots under still-photographic mode at 20°C. via an LCD monitoring screen without strobe-flashing at every minute.

Discharge curve and discharge capacity of the sample batteries 1˜4 arerespectively shown in FIG. 5 and FIG. 12. Test result via loading ofsample batteries 1˜4 in the digital cameras is shown in FIG. 6.

By referring to FIG. 12 and FIG. 5, it is understood that, compared tothe alkaline manganese battery corresponding to sample 1, the first betanickel-zinc battery corresponding to sample 2, the gamma nickel-zincbattery corresponding to sample 3, and the second beta nickel-zincbattery corresponding to sample 4 respectively generate quitedistinguished discharge characteristic under heavy load. Further, asshown in FIG. 6, it is also understood that those batteriescorresponding to samples 2˜4 are respectively durable to use for alonger period of time than the alkaline-manganese battery correspondingto sample 1 even when actually being loaded in a compact-size portableelectronic apparatus.

Compared to the gamma nickel-zinc battery as sample 3 and the secondbeta nickel-zinc battery as sample 4, the first beta nickel-zinc batteryas sample 2 generates more distinguished discharge characteristic.Inasmuch as the nickel oxyhydroxide contained in the sample 2 is of thehighest density, it is thus conceived that the sample 2 contains agreater weight of positive electrode mixture per battery than that ofthe samples 3 and 4, in other words, the sample 2 contains a greatercapacity of the positive electrode.

Next, specific surface area of the positive electrode active material isdescribed below.

Initially, beta-type nickel oxyhydroxide comprising substantiallyspherical particles were generated by chemically oxidizing high-densitynickel hydroxide, where the high-density nickel hydroxide was composedof substantially spherical particles based on 2.3 g/cm³ of tap densityand 1.8 g/cm³ of bulk density; the above chemical oxidizing process wasexecuted in alkaline solution containing sodium hypochlorite. A varietyof beta-type nickel oxyhydroxides with specific surface area in a rangeof 1˜60 m²/g based on BET method were prepared. Next, based on 85:8:7 ofweight ratio, the prepared beta-type nickel oxyhydroxides, graphite, andaqueous solution of potassium hydride (40% by weight), were fully mixedwith each other before completing production of positive electrodemixture. Like the preceding sample 2, a number of “AA”-size formatcompact alkaline batteries were prepared as samples 5˜20.

In addition, as in the above description, gamma-type nickeloxyhydroxides were generated by chemical oxidation. A variety ofgamma-type nickel oxyhydroxide with specific surface area in a range of3˜50 m²/g based on BET method were prepared. Except for those which wereused for composing a positive electrode active material, as in thesample 3, “AA”-size format alkaline batteries were prepared as samples21˜24.

In addition, by electrolytically oxidizing conventional nickelhydroxide, a variety of beta-type nickel oxyhydroxides having specificsurface area in a range of 3˜50 m²/g based on BET method were prepared.Except for those which were used for composing positive electrode activematerial, like the preceding sample 4, “AA”-size format compact alkalinebatteries were prepared as samples 25˜28.

Next, discharge test was executed against the prepared samples 5˜28 bycontinuously discharging voltage until reaching 1.0V at 1500 mW ofconstant power at 20° C. of atmospheric temperature. One of thedischarge tests was executed against those sample batteries aged for twoweeks at 20° C. after the formation of batteries. Other tests wereexecuted against those which were stored for 20 days at 60° C. ofatmosphere after elapsing two weeks of initial storage period at 20° C.from the date of completing production thereof.

Results of discharge test executed against samples 5˜28 are shown inFIG. 13 and FIGS. 7˜9.

By referring to FIG. 13 and FIGS. 7˜9, as a result of testing samples5˜20 comprising beta-type nickel oxyhydroxides for composing a positiveelectrode via chemical oxidation process, it is understood that samples7˜18 utilizing beta-type nickel oxyhydroxide each having 3˜50 m²/g ofspecific surface area based on BET method respectively generate quitedistinguished discharge characteristic under heavy load and durablestorage characteristic. On the other hand, despite of satisfactorystorage characteristic, those samples 21˜24 utilizing gamma-type nickeloxyhydroxide for composing a positive electrode via chemical oxidationprocess respectively fail to generate distinguished dischargecharacteristic under heavy load. Conversely, despite of sufficientdischarge characteristic under heavy load, those samples 25˜28 utilizingbeta-type nickel oxyhydroxide for composing positive electrode viaelectrolytic oxidation process respectively prove to be noticeably poorin the storage durability.

Based on the above results, it is understood that, in terms of thenickel-zinc battery related to the present invention, beta-type nickeloxyhydroxide generated via chemical oxidation of high-density nickelhydroxide should desirably be utilized for composing positive electrodeactive material. It is further understood that use of such a beta-typenickel oxyhydroxide having own specific surface area within a range of3˜50 m²/g via BET method is desirable.

Next, a method of treating beta-type nickel oxyhydroxide in alkalinesolution is described below.

Initially, beta-type nickel oxyhydroxide generated by chemical oxidationof high-density nickel hydroxide was mixed with aqueous solution ofpotassium hydroxide, and then, adjustment was effected against densityof aqueous solution of potassium hydroxide, mixing temperature, mixingtime, and mixing pressure. It was so arranged that net contents ofpotassium in the final formulation of the beta-type nickel oxyhydroxideprecisely range from 0.5% by weight to a maximum of 5.0% by weight. Notethat the above-referred high-density nickel hydroxide was composed ofsubstantially spherical particles based on 2.3 g/cm³ of tap density and1.8 g/cm³ of bulk density. The above chemical oxidation process wasexecuted in alkaline solution containing sodium hypochlorite. Theresultant beta-type nickel oxyhydroxide was composed of substantiallyspherical particles each having 20 μm of mean particle size based on 2.5g/cm³ of tap density, 2.0 g/cm³ of bulk density, and 5˜70 μm of gradingdistribution. The processing condition is shown in FIG. 14.

During the test, whenever pressurizing process was required, reaction isimplemented via an autoclave. The beta-type nickel oxyhydroxide andpotassium hydroxide (40% by weight) prior to treatment were arranged tobe 1:5 of weight ratio. After completing the treatment, separation andwashing were executed against the beta-type nickel oxyhydroxide.

It is desired that concentration of potassium hydroxide be in a rangefrom 30% by weight to a maximum of 45% by weight. If concentration ofpotassium remains below 30% by weight, then it will become difficult toterminate reaction. On the other hand, it is quite hard to procure suchpotassium hydroxide aqueous solution having more than 45% by weight ofconcentration from industrial sources.

Assuming that potassium hydroxide has 40% by weight of concentration forexample, in terms of weight ratio between beta-type nickel oxyhydroxideand potassium hydroxide prior to the treatment, it is desired thatweight ratio of potassium hydroxide remain within a range from 3 to 10against 1 of that of beta-type nickel oxyhydroxide. This is because, ifthe weight ratio is less than 3, then, it will become difficult toterminate reaction. Conversely, if the weight ratio exceeds 10, it willentail difficulty to separate and wash the beta-type nickel oxyhydroxideafter completing a reaction process. Further, as is obvious from FIG.14, it is desired that reaction temperature be held within a range of40° C.˜60° C. Further, it is also desired that reaction time be heldwithin a range of approximately 10 hours˜60 hours. Further, it is alsodesired that reaction pressure be held within a range from normalpressure to a maximum of 0.9 Mpa.

Test result evidenced that the form of the beta-type nickel oxyhydroxideimpregnated with alkaline cation between layers produced via theabove-referred alkaline treatment was substantially identical to that ofthe other beta-type nickel oxyhydroxide generated via chemical oxidationof high-density nickel hydroxide.

Further, test result evidenced that mean particle size, gradingdistribution, bulk density, and tap density of the beta-type nickeloxyhydroxide containing alkaline cation were substantially identical tothose of the other beta-type nickel oxyhydroxide generated via chemicaloxidation of high-density nickel hydroxide.

Next, based on the composition shown in FIG. 15, a positive electrodemixture was prepared by fully mixing the beta-type nickel oxyhydroxidegenerated via chemical oxidation of high-density nickel hydroxide, theother beta-type nickel oxyhydroxide generated via an alkaline treatmentprocess, graphite powder, and aqueous solution of potassium hydroxide.Note that the graphite power is formulated as high-purity graphitepowder comprising 6 μm of mean particle size, 1˜25 μm of gradingdistribution, and a maximum of 0.3% by weight of ash component. Then,like the above example, a number of “AA”-size format alkaline batterieswere produced as samples 29˜39.

Sample 29 was prepared with the beta-type nickel oxyhydroxide generatedvia chemical oxidation of high-density nickel hydroxide. Samples 30˜39were respectively prepared with the other beta-type nickel oxyhydroxidecomplete with the above alkaline treatment. FIG. 15 designatescomposition (% by weight) of component materials for composing thepositive electrode, composition (% by weight) of potassium dispersed inthe beta-type nickel oxyhydroxide, and filling amount (gram) of thepositive electrode mixture per battery. Composition (% by weight) ofpotassium dispersed in the beta-type nickel oxyhydroxide wasquantitatively analyzed by applying an atomic light-absorptive analysismethod.

Those batteries corresponding to samples 29˜39 were then stored for 20days at 60° C., and then treated with a discharge test until the voltagereached 1.0V at 100 mW, 500 mW, 1000 mW, and 1500 mW of constant power.Discharge capacity of batteries corresponding to samples 29˜39 beforeand after storage is shown in FIG. 16, FIG. 17, and FIG. 10.

By referring to FIG. 16 and FIG. 10, it is evidenced that thosebatteries corresponding to samples 29˜39 prior to storage respectivelygenerated a substantially identical value of discharge capacity at 100mW, 500 mW, 1000 mW, and 1500 mW of constant power.

By referring to FIG. 16, FIG. 17, and FIG. 10, it is understood that,compared to the sample 29 comprising the beta-type nickel oxyhydroxidegenerated via chemical oxidation of high-density nickel hydroxide, thesample 33 incorporating more than 2% by weight of potassium in thebeta-type nickel oxyhydroxide incurred less degradation of capacityafter storage as a result of treatment with alkaline solution. It wasfurther clarified from the test results of samples 35˜39 that furtherdegradation of capacity could be prevented from occurrence by way ofproviding a minimum of 3% by weight of potassium composition. When thereis a maximum of 2% by weight of potassium composition in the beta-typenickel oxyhydroxide, improved effect can hardly be generated in thestorage characteristic of batteries. Conceivably, inasmuch as the amountof potassium ion infiltrated between layers of the beta-type nickeloxyhydroxide via an alkaline treatment remains short, potassium ionpresent in electrolytic solution is absorbed into the beta-type nickeloxyhydroxide during storage, whereby causing concentration of theelectrolytic solution to be diluted.

The above description has solely referred to the case in which aqueoussolution of potassium hydroxide was utilized for executing an alkalinetreatment process. However, according to the test result, substantiallyidentical results were also generated even when utilizing aqueoussolution of lithium hydroxide and aqueous solution of sodium hydroxideas well. Based on this result, it is conceived that substantiallyidentical results will also be secured even when utilizing thesealkaline aqueous solutions via mixture and even when more than two kindsof alkaline cations are mixed together inside of the lattice of thebeta-type nickel oxyhydroxide.

Based on the above result, in the formation of the nickel-zinc batteryaccording to a preferred form for embodying the present invention, it isclarified from the process for enabling alkaline cationic seed toinfiltrate itself between layers of the beta-type nickel oxyhydroxidethat composition of the alkaline cationic seed after completion of theprocess should desirably be arranged to be in a range from 2% by weightto a maximum of 5% by weight, more preferably, in a range from 3% byweight to a maximum of 5% by weight before utilizing the beta-typenickel oxyhydroxide to serve as the positive electrode active material.

The above description related to the above-referred alkaline treatmenthas solely referred to the beta-type nickel oxyhydroxide comprisingsubstantially spherical particles. It should be understood, however thatthe form of the beta-type nickel oxyhydroxide is not solely limited tothe above substantially spherical configuration, but the presentinvention is also applicable to a variety of forms other than thespherical configuration as well.

Next, the amount of contents of graphite formulated in the positiveelectrode mixture is described below.

Initially, based on the composition shown in FIG. 18, beta-type nickeloxyhydroxide generated via chemical oxidation of high-density nickelhydroxide, graphite, and 40% by weight of aqueous solution of potassiumhydroxide, were fully mixed with each other to produce positiveelectrode mixture, and then, like the above example, a number of“AA”-size format alkaline batteries were produced as samples 40˜48. Notethat the above beta-type nickel oxyhydroxide was composed ofsubstantially spherical particles each having 20 μm of mean particlesize, based on 2.5 g/cm³ of tap density, 2.0 g/cm³ of bulk density, and5˜70 μm of grading distribution. The above-referred high-density nickelhydroxide is composed of substantially spherical particles based on 2.3g/cm³ of tap density and 1.8 g/cm³ of bulk density. The above chemicaloxidation was executed in alkaline solution containing sodiumhypochlorite. The above graphite was formulated as high-purity graphitepowder comprising 6 μm of mean particle size, 1˜25 μm of gradingdistribution, and a maximum of 0.3% of ash component.

Like the preceding examples, those batteries corresponding to samples40˜48 were respectively treated with discharge test until the voltagereached 1.0V at 1500 mW of constant power. Test results of dischargecapacity of the samples 40˜48 are shown in FIG. 19 and FIG. 11.

By referring to FIG. 19 and FIG. 11, it was clarified that better effectwas secured by adding a minimum of 4% by weight and a maximum of 8% byweight of graphite against the total weight of the positive electrode asthe proper amount to be included in the positive electrode mixture.Since nickel oxyhydroxide and nickel hydroxide as the one generated viadischarge respectively contain a low degree of electron conductivity, itis conceived that, when the graphite contents are less than 4% by weightin the positive electrode mixture, such an effect for improving electronconductivity in the positive electrode can not fully be secured. On theother hand, when the graphite contents exceed 8% by weight, despite ofenough effect to improve electron conductivity in the positiveelectrode, as a result of the decreased filling amount of nickeloxyhydroxide as the positive electrode active material, in consequence,battery capacity itself is contracted.

Based on the above results, it was clarified that the amount of graphiteto be included in the positive electrode mixture should desirably bedefined to be a minimum of 4% by weight and a maximum of 8% by weightagainst the total weight of the positive electrode.

Although the above description pertaining to practical aspects forembodying the present invention has solely referred to the nickel-zincbattery as a primary battery. It should be understood however that thescope of the present invention is by no means restricted to the primarybattery, but the scope of the present invention is also applicable toother nickel-zinc batteries serving as a secondary battery.

Further, the above description has also referred to a cylindricalnickel-zinc battery. However, the scope of the present invention is notsolely limited to the cylindrical battery, but the present invention isalso applicable to those nickel-zinc batteries with a flat shape andother shapes as well.

Further, it should also be understood that, not only the above-referredpractical aspects, but also the present invention may also introduce avariety of forms and constitutions within such a scope that does notdeviate from the essentials of the present invention.

1. A positive electrode active material comprising beta nickeloxyhydroxide, wherein said beta nickel oxyhydroxide contains between 2%by weight to 5% by weight of alkaline cations.
 2. The positive electrodeactive material according to claim 1, wherein said beta-type nickeloxyhydroxide comprises substantially spherical particles.
 3. Thepositive electrode active material according to claim 1, wherein saidalkaline cation substance comprises any one of or a combination of morethan two selected from a group comprising Li+, Na+, and K+.
 4. Anickel-zinc battery comprising: a positive electrode comprising mixedpowder containing at least beta-type nickel oxyhydroxide being apositive electrode active material and graphite powder being an electricconductive agent; a negative electrode comprising gelled compoundcontaining at least zinc being a negative electrode active material,electrolytic solution, and gelling agent for uniformly dispersing zincand electrolytic solution; and a separator being disposed between saidpositive electrode and said negative electrode; wherein: said beta-typenickel oxyhydroxide has alkaline cation between its own layers.
 5. Thenickel-zinc battery according to claim 4, wherein said beta-type nickeloxyhydroxide comprises substantially spherical particles.
 6. Thenickel-zinc battery according to claim 4, wherein said alkaline cationsubstance comprises any one of or a combination of more than twoselected from a group comprising Li+, Na+, and K+.
 7. The nickel-zincbattery according to claim 4, wherein said beta-type nickel oxyhydroxidecontains 2% by weight to a maximum of 5% by weight of alkaline cationsubstance therein.
 8. The nickel-zinc battery according to claim 4,wherein said battery comprises a first part, a second part and a thirdpart, and, wherein: the second part is contiguous to the externalsurface of the first part, the third part is contiguous to the externalsurface of the second part, the first part contains the negativeelectrode material, the second part contains the separator, and thethird part contains the positive electrode material.
 9. The nickel-zincbattery according to claim 4, wherein said positive electrode mixedpowder contains 4% by weight to 8% by weight of graphite powder.